Even though To Sir, With Love (Khun Chai) is in the style of a traditional lakorn (in lieu of a modern BL series), both shows are set in the past with Memoire of Rati being set in the late 1910s, while Khun Chai is set in the 1940s. Though only the trailer has been released for Memoire of Rati, it is very clear there will be an attempt at an arranged marriage, struggles of the acceptance of homosexuality, and a deep wholesome love. These are qualities shared by both shows. Furthermore, they also share similar clothing with European influence is both, although Memoire of Rati is much more Thai in influence, while Khun Chai has heavy Chinese influence. Overall, if you are looking forward to watch this drama, I would highly recommend Khun Chai.
The dramas are set in very similar time periods in Thai history, with Memoire of Rati being set in the late 1910s in what seems to be somewhere in Central Thailand, while I Feel You Linger in the Air is set in the 1920s-30s in Northern Thailand. The aesthetics of both shows are very similar. Even though only the trailer has come out for Memoir of Rati, one can already tell the similarities of the two shows via the clothing, architectural style, European influence, and a more conservative form of love.
Both are historical Thai dramas happening in similar time-periods with I Feel You Linger in the Air happening in the 1920s, whereas Khun Chai is happening in the 1940s.